A major problem in cancer chemotherapy is the emergence of drug- resistant cells. Chemotherapy-resistance is probably due to multiple mechanisms including altered uptake/excretion drug, increased inactivation of drug, and altered host response such as increased DNA repair. As outlined in project number Z0l CM 06380- 02 RC, we have isolated a variety of mammalian cDNA clones which code for transcripts specifically induced by DNA damage. We have initiated studies with a variety of human tumor cells lines which have been selected for resistance to cis-Pt diamminedichloride (DDP), nitrogen mustard (HN2), or other alkylating agents. Our initial studies have involved determining the level of different stress-induced transcripts in these chemoresistant tumor cell lines compared to their parent cell lines with normal sensitivity. When this was done with P-388 cells of the mdr phenotype, a marked increased in mdr RNA compared to the parent line was observed; probes used included the rodent cDNA isolated by Ling and the human cDNA isolated by Gottesman. None of our DDI transcripts were elevated in this P-388 line. In contrast, there were multiple examples of over-expression of certain of our DDI transcripts in DDP and alkylating agent resistant cells. For example, in the case of DDIA33 RNA, this transcript was constitutively elevated in both DDP, melphalan, and HN2 resistant human tumor cell lines and also in a MNNG resistant hamster cell line. It should be noted that these cell lines were not of mdr phenotype and mdr RNA was not increased. The levels of different hsp (heat shock protein) transcripts were determined also and no increased expression was found. These studies raise the important possibility that over- expression of certain DNA-damage-inducible genes may play a role in chemotherapy resistance.